U.S. patent application number 13/670977 was filed with the patent office on 2013-05-16 for method and apparatus for soft buffer management for harq operation.
This patent application is currently assigned to QUALCOMM INCORPORATED. The applicant listed for this patent is QUALCOMM INCORPORATED. Invention is credited to Wanshi Chen, Jelena Damnjanovic, Peter Gaal, Juan Montojo.
Application Number | 20130121216 13/670977 |
Document ID | / |
Family ID | 48280566 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130121216 |
Kind Code |
A1 |
Chen; Wanshi ; et
al. |
May 16, 2013 |
METHOD AND APPARATUS FOR SOFT BUFFER MANAGEMENT FOR HARQ
OPERATION
Abstract
Certain aspects of the present disclosure propose a method and
an apparatus for calculating maximum number of hybrid automatic
repeat request (HARQ) processes per component carrier and/or number
of soft buffer bits for HARQ operation by taking into account the
subframes which are available for a physical downlink shared
channel (PDSCH) for a user equipment (UE) or a group of UEs. In the
proposed method, the subframes that are not available for a PDSCH
for at least a UE (either by specification or by configuration) may
not be considered in calculating the number of soft buffer
bits.
Inventors: |
Chen; Wanshi; (San Diego,
CA) ; Gaal; Peter; (San Diego, CA) ;
Damnjanovic; Jelena; (Del Mar, CA) ; Montojo;
Juan; (Nuremberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM INCORPORATED; |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
48280566 |
Appl. No.: |
13/670977 |
Filed: |
November 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61558795 |
Nov 11, 2011 |
|
|
|
Current U.S.
Class: |
370/280 ;
370/329 |
Current CPC
Class: |
H04L 5/0005 20130101;
H04L 5/003 20130101; H04L 1/1835 20130101; H04L 27/2601
20130101 |
Class at
Publication: |
370/280 ;
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04; H04J 3/00 20060101 H04J003/00 |
Claims
1. A method for wireless communications, comprising: determining,
for each component carrier, a number of downlink subframes
available for a physical downlink shared channel (PDSCH); and
determining at least one of a maximum number of downlink hybrid
automatic repeat request (HARQ) processes or a size of a soft
buffer based at least on the number of downlink subframes available
for PDSCH, wherein the downlink subframes unavailable for a PDSCH
are not considered.
2. The method of claim 1, wherein the downlink subframes
unavailable for a PDSCH comprise one or more subframes unavailable
for a PDSCH either by specification or by configuration.
3. The method of claim 2, wherein the downlink subframes
unavailable for a PDSCH comprise special subframes that are
configured not to transmit any PDSCH in time division duplex (TDD)
mode.
4. The method of claim 2, wherein the downlink subframes
unavailable for a PDSCH comprise multimedia broadcast over a single
frequency network (MBSFN) subframes.
5. The method of claim 1, wherein the number of downlink subframes
available for PDSCH is the same for a plurality of user
equipments.
6. The method of claim 1, wherein the number of downlink subframes
available for PDSCH is determined for a first user equipment (UE)
and a second UE, wherein the number of subframes available for
PDSCH is specific to each of the first and the second UEs.
7. The method of claim 6, wherein a downlink subframe is determined
to be available for a PDSCH for the first UE, and is determined to
be unavailable for a PDSCH for the second UE.
8. The method of claim 1, wherein a UE is configured to communicate
via two or more component carriers comprising a primary component
carrier and one or more secondary component carriers, wherein the
size of the soft buffer is determined for the one or more secondary
component carriers.
9. The method of claim 8, wherein the primary component carrier is
in compliance with a first release of a standard and the secondary
component carriers are in compliance with a second release of the
standard later than the first release.
10. The method of claim 1, wherein the size of the soft buffer is
determined for one or more extension carriers.
11. The method of claim 1, wherein the size of the soft buffer is
different for different component carriers.
12. An apparatus for wireless communications, comprising: means for
determining, for each component carrier, a number of downlink
subframes available for a physical downlink shared channel (PDSCH);
and means for determining at least one of a maximum number of
downlink hybrid automatic repeat request (HARQ) processes or a size
of a soft buffer based at least on the number of downlink subframes
available for PDSCH, wherein the downlink subframes unavailable for
a PDSCH are not considered.
13. The apparatus of claim 12, wherein the downlink subframes
unavailable for a PDSCH comprise one or more subframes unavailable
for a PDSCH either by specification or by configuration.
14. The apparatus of claim 13, wherein the downlink subframes
unavailable for a PDSCH comprise special subframes that are
configured not to transmit any PDSCH in time division duplex (TDD)
mode.
15. The apparatus of claim 13, wherein the downlink subframes
unavailable for a PDSCH comprise multimedia broadcast over a single
frequency network (MBSFN) subframes.
16. The apparatus of claim 12, wherein the number of downlink
subframes available for PDSCH is the same for a plurality of user
equipments.
17. The apparatus of claim 12, wherein the number of downlink
subframes available for PDSCH is determined for a first user
equipment (UE) and a second UE, wherein the number of subframes
available for PDSCH is specific to each of the first and the second
UEs.
18. The apparatus of claim 17, wherein a downlink subframe is
determined to be available for a PDSCH for the first UE, and is
determined to be unavailable for a PDSCH for the second UE.
19. The apparatus of claim 12, wherein a UE is configured to
communicate via two or more component carriers comprising a primary
component carrier and one or more secondary component carriers,
wherein the size of the soft buffer is determined for the one or
more secondary component carriers.
20. The apparatus of claim 19, wherein the primary component
carrier is in compliance with a first release of a standard and the
secondary component carriers are in compliance with a second
release of the standard later than the first release.
21. The apparatus of claim 12, wherein the size of the soft buffer
is determined for one or more extension carriers.
22. The apparatus of claim 12, wherein the size of the soft buffer
is different for different component carriers.
23. A computer-program product, comprising a non-transitory
computer readable medium having instructions stored thereon, the
instructions being executable by one or more processors and the
instructions comprising: instructions for determining, for each
component carrier, a number of downlink subframes available for a
physical downlink shared channel (PDSCH); and instructions for
determining at least one of a maximum number of downlink hybrid
automatic repeat request (HARQ) processes or a size of a soft
buffer based at least on the number of downlink subframes available
for PDSCH, wherein the downlink subframes unavailable for a PDSCH
are not considered.
24. An apparatus, comprising: at least one processor configured to:
determine, for each component carrier, a number of downlink
subframes available for a physical downlink shared channel (PDSCH),
and determine at least one of a maximum number of downlink hybrid
automatic repeat request (HARQ) processes or a size of a soft
buffer based at least on the number of downlink subframes available
for PDSCH, wherein the downlink subframes unavailable for a PDSCH
are not considered; and a memory coupled to the at least one
processor.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119
[0001] The present Application for Patent claims priority to U.S.
Provisional Application No. 61/558,795, entitled, "Method and
Apparatus for Soft Buffer Management for HARQ Operation," filed
Nov. 11, 2011, and assigned to the assignee hereof, which is hereby
expressly incorporated by reference herein.
TECHNICAL FIELD
[0002] Certain embodiments of the present disclosure generally
relate to wireless communications and, more particularly, to
managing soft buffers in hybrid automatic repeat request (HARQ)
operation.
BACKGROUND
[0003] Wireless communication systems are widely deployed to
provide various types of communication content such as voice, data,
and so on. These systems may be multiple-access systems capable of
supporting communication with multiple users by sharing the
available system resources (e.g., bandwidth and transmit power).
Examples of such multiple-access systems include code division
multiple access (CDMA) systems, time division multiple access
(TDMA) systems, frequency division multiple access (FDMA) systems,
3GPP Long Term Evolution (LTE) systems, and orthogonal frequency
division multiple access (OFDMA) systems.
[0004] Generally, a wireless multiple-access communication system
can simultaneously support communication for multiple wireless
terminals. Each terminal communicates with one or more base
stations via transmissions on the forward and reverse links. The
forward link (or downlink) refers to the communication link from
the base stations to the terminals, and the reverse link (or
uplink) refers to the communication link from the terminals to the
base stations. This communication link may be established via a
single-input-single-output, multiple-input-single-output or a
multiple-input-multiple-output (MIMO) system.
[0005] A MIMO system employs multiple (N.sub.T) transmit antennas
and multiple (N.sub.R) receive antennas for data transmission. A
MIMO channel formed by the N.sub.T transmit and N.sub.R receive
antennas may be decomposed into N.sub.S independent channels, which
are also referred to as spatial channels, where N.sub.S.ltoreq.min
{N.sub.T, N.sub.R}. Each of the N.sub.S independent channels
corresponds to a dimension. The MIMO system can provide improved
performance (e.g., higher throughput and/or greater reliability) if
the additional dimensionalities created by the multiple transmit
and receive antennas are utilized.
[0006] A MIMO system may support time division duplex (TDD) and/or
frequency division duplex (FDD) systems. In a TDD system, the
forward and reverse link transmissions are on the same frequency
region so that the reciprocity principle allows the estimation of
the forward link channel from the reverse link channel. This
enables the base station to extract transmit beamforming gain on
the forward link when multiple antennas are available at the base
station. In an FDD system, forward and reverse link transmissions
are on different frequency regions.
SUMMARY
[0007] Certain aspects of the present disclosure provide a method
for wireless communications. The method generally includes
determining, for each component carrier, a number of downlink
subframes available for a physical downlink shared channel (PDSCH),
and determining at least one of a maximum number of downlink hybrid
automatic repeat request (HARQ) processes or a size of a soft
buffer based at least on the number of downlink subframes available
for PDSCH, wherein the downlink subframes unavailable for a PDSCH
are not considered.
[0008] Certain aspects of the present disclosure provide an
apparatus for wireless communications. The apparatus generally
includes means for determining, for each component carrier, a
number of downlink subframes available for a physical downlink
shared channel (PDSCH), and means for determining at least one of a
maximum number of downlink hybrid automatic repeat request (HARQ)
processes or a size of a soft buffer based at least on the number
of downlink subframes available for PDSCH, wherein the downlink
subframes unavailable for a PDSCH are not considered.
[0009] Certain aspects provide a computer-program product for
wireless communications, comprising a non-transitory
computer-readable medium having instructions stored thereon, the
instructions being executable by one or more processors. The
instructions generally include instructions for determining, for
each component carrier, a number of downlink subframes available
for a physical downlink shared channel (PDSCH), and instructions
for determining at least one of a maximum number of downlink hybrid
automatic repeat request (HARQ) processes or a size of a soft
buffer based at least on the number of downlink subframes available
for PDSCH, wherein the downlink subframes unavailable for a PDSCH
are not considered.
[0010] Certain aspects of the present disclosure provide an
apparatus for wireless communications. The apparatus generally
includes at least one processor and a memory coupled to the at
least one processor. The processor is configured to determine, for
each component carrier, a number of downlink subframes available
for a physical downlink shared channel (PDSCH), and determine at
least one of a maximum number of downlink hybrid automatic repeat
request (HARQ) processes or a size of a soft buffer based at least
on the number of downlink subframes available for PDSCH, wherein
the downlink subframes unavailable for a PDSCH are not
considered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above-recited features of
the present disclosure can be understood in detail, a more
particular description, briefly summarized above, may be had by
reference to aspects, some of which are illustrated in the appended
drawings. It is to be noted, however, that the appended drawings
illustrate only certain typical aspects of this disclosure and are
therefore not to be considered limiting of its scope, for the
description may admit to other equally effective aspects.
[0012] FIG. 1 illustrates a multiple access wireless communication
system, in accordance with certain embodiments of the present
disclosure.
[0013] FIG. 2 illustrates a block diagram of a communication
system, in accordance with certain embodiments of the present
disclosure.
[0014] FIG. 3 is a block diagram conceptually illustrating an
example of a frame structure in a wireless communications network
in accordance with certain aspects of the present disclosure.
[0015] FIG. 4 illustrates a table including different user
equipment (UE) categories and their corresponding parameters, as
described in the long term evolution (LTE) standard.
[0016] FIG. 5 illustrates a table containing maximum number of
downlink (DL) hybrid automatic repeat request (HARQ) processes for
each time division duplex (TDD) uplink (UL)/DL configuration as
described in Release-10 of the LTE standard.
[0017] FIG. 6 illustrates example operations that may be performed
by a user equipment or a base station for soft buffer management in
hybrid automatic repeat request (HARQ) operation, in accordance
with certain aspects of the present disclosure.
[0018] FIG. 7 illustrates an example table showing the benefits of
the proposed soft buffer management, in accordance with certain
aspects of the present disclosure.
[0019] FIG. 8 illustrates an example network comprising a base
station and a user equipment, in accordance with certain aspects of
the present disclosure.
DETAILED DESCRIPTION
[0020] Various aspects are now described with reference to the
drawings. In the following description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of one or more aspects. It may be
evident; however, that such aspect(s) may be practiced without
these specific details.
[0021] As used in this application, the terms "component,"
"module," "system" and the like are intended to include a
computer-related entity, such as but not limited to hardware,
firmware, a combination of hardware and software, software, or
software in execution. For example, a component may be, but is not
limited to being, a process running on a processor, a processor, an
object, an executable, a thread of execution, a program and/or a
computer. By way of illustration, both an application running on a
computing device and the computing device can be a component. One
or more components can reside within a process and/or thread of
execution and a component may be localized on one computer and/or
distributed between two or more computers. In addition, these
components can execute from various computer readable media having
various data structures stored thereon. The components may
communicate by way of local and/or remote processes such as in
accordance with a signal having one or more data packets, such as
data from one component interacting with another component in a
local system, distributed system, and/or across a network such as
the Internet with other systems by way of the signal.
[0022] Furthermore, various aspects are described herein in
connection with a terminal, which can be a wired terminal or a
wireless terminal A terminal can also be called a system, device,
subscriber unit, subscriber station, mobile station, mobile, mobile
device, remote station, remote terminal, access terminal, user
terminal, communication device, user agent, user device, or user
equipment (UE). A wireless terminal may be a cellular telephone, a
satellite phone, a cordless telephone, a Session Initiation
Protocol (SIP) phone, a wireless local loop (WLL) station, a
personal digital assistant (PDA), a handheld device having wireless
connection capability, a computing device, or other processing
devices connected to a wireless modem. Moreover, various aspects
are described herein in connection with a base station. A base
station may be utilized for communicating with wireless terminal(s)
and may also be referred to as an access point, a Node B, or some
other terminology.
[0023] Moreover, the term "or" is intended to mean an inclusive
"or" rather than an exclusive "or." That is, unless specified
otherwise, or clear from the context, the phrase "X employs A or B"
is intended to mean any of the natural inclusive permutations. That
is, the phrase "X employs A or B" is satisfied by any of the
following instances: X employs A; X employs B; or X employs both A
and B. In addition, the articles "a" and "an" as used in this
application and the appended claims should generally be construed
to mean "one or more" unless specified otherwise or clear from the
context to be directed to a singular form.
[0024] The techniques described herein may be used for various
wireless communication networks such as Code Division Multiple
Access (CDMA) networks, Time Division Multiple Access (TDMA)
networks, Frequency Division Multiple Access (FDMA) networks,
Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA)
networks, etc. The terms "networks" and "systems" are often used
interchangeably. A CDMA network may implement a radio technology
such as Universal Terrestrial Radio Access (UTRA), CDMA 2000, etc.
UTRA includes Wideband-CDMA (W-CDMA). CDMA2000 covers IS-2000,
IS-95 and IS-856 standards. A TDMA network may implement a radio
technology such as Global System for Mobile Communications
(GSM).
[0025] An OFDMA network may implement a radio technology such as
Evolved UTRA (E-UTRA), The Institute of Electrical and Electronics
Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM.RTM.,
etc. UTRA, E-UTRA, and GSM are part of Universal Mobile
Telecommunication System (UMTS). Long Term Evolution (LTE) is a
recent release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS
and LTE are described in documents from an organization named "3rd
Generation Partnership Project" (3GPP). CDMA2000 is described in
documents from an organization named "3rd Generation Partnership
Project 2" (3GPP2). These various radio technologies and standards
are known in the art. For clarity, certain aspects of the
techniques are described below for LTE, and LTE terminology is used
in much of the description below. It should be noted that the LTE
terminology is used by way of illustration and the scope of the
disclosure is not limited to LTE. Rather, the techniques described
herein may be utilized in various applications involving wireless
transmissions, such as personal area networks (PANs), body area
networks (BANs), location, Bluetooth, GPS, UWB, RFID, and the like.
Further, the techniques may also be utilized in wired systems, such
as cable modems, fiber-based systems, and the like.
[0026] Single carrier frequency division multiple access (SC-FDMA),
which utilizes single carrier modulation and frequency domain
equalization has similar performance and essentially the same
overall complexity as those of an OFDMA system. SC-FDMA signal may
have lower peak-to-average power ratio (PAPR) because of its
inherent single carrier structure. SC-FDMA may be used in the
uplink communications where lower PAPR greatly benefits the mobile
terminal in terms of transmit power efficiency. SC-FDMA is
currently a working assumption for uplink multiple access scheme in
3GPP Long Term Evolution (LTE), or Evolved UTRA.
[0027] Referring to FIG. 1, a multiple access wireless
communication system 100 according to one aspect is illustrated. An
access point 102 (AP) includes multiple antenna groups, one
including 104 and 106, another including 108 and 110, and an
additional including 112 and 114. In FIG. 1, only two antennas are
shown for each antenna group, however, more or fewer antennas may
be utilized for each antenna group. Access terminal 116 (AT) is in
communication with antennas 112 and 114, where antennas 112 and 114
transmit information to access terminal 116 over forward link 118
and receive information from access terminal 116 over reverse link
120. Access terminal 122 is in communication with antennas 104 and
106, where antennas 104 and 106 transmit information to access
terminal 122 over forward link 124 and receive information from
access terminal 122 over reverse link 126. In a Frequency Division
Duplex (FDD) system, communication links 118, 120, 124 and 126 may
use a different frequency for communication. For example, forward
link 118 may use a different frequency than that used by reverse
link 120.
[0028] Each group of antennas and/or the area in which they are
designed to communicate is often referred to as a sector of the
access point. In an aspect, antenna groups each are designed to
communicate to access terminals in a sector of the areas covered by
access point 102.
[0029] In communication over forward links 118 and 124, the
transmitting antennas of access point 102 utilize beamforming in
order to improve the signal-to-noise ratio of forward links for the
different access terminals 116 and 122. Also, an access point using
beamforming to transmit to access terminals scattered randomly
through its coverage causes less interference to access terminals
in neighboring cells than an access point transmitting through a
single antenna to all its access terminals.
[0030] An access point may be a fixed station used for
communicating with the terminals and may also be referred to as a
Node B, an evolved Node B (eNB), or some other terminology. An
access terminal may also be called a mobile station, user equipment
(UE), a wireless communication device, terminal, or some other
terminology. For certain aspects, either the AP 102 or the access
terminals 116, 122 may utilize an interference cancellation
technique as described herein to improve performance of the
system.
[0031] FIG. 2 is a block diagram of an aspect of a transmitter
system 210 and a receiver system 250 in a MIMO system 200. At the
transmitter system 210, traffic data for a number of data streams
is provided from a data source 212 to a transmit (TX) data
processor 214. An embodiment of the present disclosure is also
applicable to a wireline (wired) equivalent system of FIG. 2
[0032] In an aspect, each data stream is transmitted over a
respective transmit antenna. TX data processor 214 formats, codes,
and interleaves the traffic data for each data stream based on a
particular coding scheme selected for that data stream to provide
coded data.
[0033] The coded data for each data stream may be multiplexed with
pilot data using OFDM techniques. The pilot data is typically a
known data pattern that is processed in a known manner and may be
used at the receiver system to estimate the channel response. The
multiplexed pilot and coded data for each data stream is then
modulated (e.g., symbol mapped) based on a particular modulation
scheme (e.g., Binary Phase Shift Keying (BPSK), Quadrature Phase
Shift Keying (QPSK), M-PSK in which M may be a power of two, or
M-QAM (Quadrature Amplitude Modulation)) selected for that data
stream to provide modulation symbols. The data rate, coding and
modulation for each data stream may be determined by instructions
performed by processor 230 that may be coupled with a memory
232.
[0034] The modulation symbols for all data streams are then
provided to a TX MIMO processor 220, which may further process the
modulation symbols (e.g., for OFDM). TX MIMO processor 220 then
provides N.sub.T modulation symbol streams to N.sub.T transmitters
(TMTR) 222a through 222t. In certain aspects, TX MIMO processor 220
applies beamforming weights to the symbols of the data streams and
to the antenna from which the symbol is being transmitted.
[0035] Each transmitter 222 receives and processes a respective
symbol stream to provide one or more analog signals, and further
conditions (e.g., amplifies, filters, and upconverts) the analog
signals to provide a modulated signal suitable for transmission
over the MIMO channel. N.sub.T modulated signals from transmitters
222a through 222t are then transmitted from N.sub.T antennas 224a
through 224t, respectively.
[0036] At receiver system 250, the transmitted modulated signals
are received by N.sub.R antennas 252a through 252r and the received
signal from each antenna 252 is provided to a respective receiver
(RCVR) 254a through 254r. Each receiver 254 conditions (e.g.,
filters, amplifies, and downconverts) a respective received signal,
digitizes the conditioned signal to provide samples, and further
processes the samples to provide a corresponding "received" symbol
stream.
[0037] An RX data processor 260 then receives and processes the
N.sub.R received symbol streams from N.sub.R receivers 254 based on
a particular receiver processing technique to provide N.sub.T
"detected" symbol streams. The RX data processor 260 then
demodulates, deinterleaves and decodes each detected symbol stream
to recover the traffic data for the data stream. The processing by
RX data processor 260 is complementary to that performed by TX MIMO
processor 220 and TX data processor 214 at transmitter system 210.
As described in further detail below, the RX data processor 260 may
utilize interference cancellation to cancel the interference on the
received signal.
[0038] Processor 270, coupled to a memory 272, formulates a reverse
link message. The reverse link message may comprise various types
of information regarding the communication link and/or the received
data stream. The reverse link message is then processed by a TX
data processor 238, which also receives traffic data for a number
of data streams from a data source 236, modulated by a modulator
280, conditioned by transmitters 254a through 254r, and transmitted
back to transmitter system 210.
[0039] At transmitter system 210, the modulated signals from
receiver system 250 are received by antennas 224, conditioned by
receivers 222, demodulated by a demodulator 240 and processed by a
RX data processor 242 to extract the reserve link message
transmitted by the receiver system 250.
[0040] FIG. 3 shows an exemplary frame structure 300 for FDD in
LTE. The transmission timeline for each of the downlink and uplink
may be partitioned into units of radio frames. Each radio frame may
have a predetermined duration (e.g., 10 milliseconds (ms)) and may
be partitioned into 10 subframes with indices of 0 through 9. Each
subframe may include two slots. Each radio frame may thus include
20 slots with indices of 0 through 19. Each slot may include L
symbol periods, e.g., seven symbol periods for a normal cyclic
prefix (as shown in FIG. 3) or six symbol periods for an extended
cyclic prefix. The 2L symbol periods in each subframe may be
assigned indices of 0 through 2L-1.
[0041] In LTE, an eNB may transmit a primary synchronization signal
(PSS) and a secondary synchronization signal (SSS) on the downlink
(e.g., in the center 1.08 MHz of the system bandwidth) for each
cell supported by the eNB. The PSS and SSS may be transmitted in
symbol periods 6 and 5, respectively, in subframes 0 and 5 of each
radio frame with the normal cyclic prefix, as shown in FIG. 3. The
PSS and SSS may be used by UEs for cell search and acquisition. The
eNB may also transmit a cell-specific reference signal (CRS) across
the system bandwidth for each cell supported by the eNB. The CRS is
also known as a common reference signal. The CRS may be transmitted
in certain symbol periods of each subframe and may be used by the
UEs to perform channel estimation, channel quality measurement,
and/or other functions. The eNB may also transmit a Physical
Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of
certain radio frames. The PBCH may carry some system information.
The eNB may transmit other system information such as System
Information Blocks (SIBs) on a Physical Downlink Shared Channel
(PDSCH) in certain subframes. The eNB may transmit control
information/data on a Physical Downlink Control Channel (PDCCH) in
the first B symbol periods of a subframe, where B may be
configurable for each subframe. The eNB may transmit traffic data
and/or other data on the PDSCH in the remaining symbol periods of
each subframe.
[0042] The wireless network may support hybrid automatic
retransmission (HARQ) for data transmission on the downlink and
uplink. For HARQ, a transmitter (e.g., an eNB) may send one or more
transmissions of a packet until the packet is decoded correctly by
a receiver (e.g., a UE) or some other termination condition is
encountered. For synchronous HARQ, all transmissions of the packet
may be sent in subframes of a single interlace. For asynchronous
HARQ, each transmission of the packet may be sent in any
subframe.
An Example Soft Buffer Management for HARQ Operation
[0043] In wireless communication systems, the data associated with
one or more received messages may be stored in soft buffer memory.
The soft buffer memory stores soft information associated with
received bits, which are also referred to as soft bits. The soft
information for a received bit may contain information about the
most likely value of the bit and a measure of its reliability. The
term "soft information" or "soft bit" generally refers to not
making a hard decision about the value of a bit during demodulation
and/or input to a decoder. These measures of reliability can be
used in special soft decision decoders (e.g., Turbo decoders) to
enhance decoding performance. For example, a decoded received
packet and its supporting data (e.g., soft bits) are generally
stored in soft buffer memory to accommodate combining the data with
retransmitted data in the event that a determination is made that
the packet was received in error for a previous transmission or
previous retransmission. In a hybrid automatic retransmit request
(HARQ) scheme, the receiver may request retransmission of a packet
(or part of the packet), if the packet is not received correctly.
At the receiver, the retransmitted packet may be combined with the
originally received packet before decoding.
[0044] In 3GPP LTE, a receive buffer size may vary depending on
capability of the UE. This is to limit the receive buffer size
according to the UE capability since the increase in the receive
buffer size may result in the increase in manufacturing costs of
the UE. In particular, the maximum number of HARQ processes in
asynchronous HARQ is important due to limited soft buffer
capability of a UE. This is because the limited soft buffer size
may result in the decrease in an available buffer size per HARQ
process along with the increase in the maximum number of HARQ
processes, and as a result, channel coding performance may
decrease.
[0045] Certain aspects of the present disclosure propose a method
and an apparatus for calculating maximum number of downlink hybrid
automatic repeat request (HARQ) processes and/or size of a soft
buffer by only taking into account the subframes which are
available for PDSCH for a UE or a group of UEs. In the proposed
method, the subframes that are not available for PDSCH for at least
a UE (either by specification or by configuration) may not be
considered in calculating the size of the soft buffer (in bits)
and/or maximum number of downlink HARQ processes.
[0046] According to Release-10 of the long term evolution (LTE)
standard, a user equipment (UE) may be configured with two or more
component carriers (CCs). For example, the UE may be configured
with one downlink (DL) CC and one uplink (UL) component carrier.
Soft buffers may be used in base stations and user equipments. The
soft buffers may be managed based on number of configured CCs,
category and capabilities of the UE, maximum number of hybrid
automatic repeat request (HARQ) processes, number of transport
blocks, number of coded blocks, and other parameters.
[0047] FIG. 4 illustrates a table including different UE categories
and their corresponding parameters, as described in the LTE Rel-10
standard. A total of eight UE categories may be defined as shown in
the table. The table illustrates parameters such as maximum number
of DL-shared channel (SCH) transport block bits received within a
transmission time interval (TTI) 404, maximum number of bits of a
DL-SCH transport block received within a TTI 406, total number of
soft channel bits 408, and maximum number of supported layers for
spatial multiplexing in DL 410.
[0048] In FIG. 4, the field `UE Category` 402 defines a combined
uplink and downlink capability. The field `maximum number of DL-SCH
transport block bits received within a TTI` 404 defines the maximum
number of DLSCH transport blocks bits that the UE is capable of
receiving within a DLSCH TTI. This number does not include the bits
of a DLSCH transport block carrying broadcast control channel
(BCCH) in the same subframe. The field `maximum number of bits of a
DLSCH transport block received within a TTI` 406 defines the
maximum number of DLSCH transport block bits that the UE is capable
of receiving in a single transport block within a DLSCH TTI. The
field `total number of DLSCH soft channel bits` 408 defines the
total number of soft channel bits available for HARQ processing.
This number does not include the soft channel bits required by the
dedicated broadcast HARQ process for the decoding of system
information. The field `maximum number of supported layers for
spatial multiplexing in DL` 410 defines the maximum number of
supported layers for spatial multiplexing per UE. The UE shall
support the number of layers according to its Rel-8/9 category
(Cat. 1-5) in all non-carrier aggregation band combinations.
[0049] For soft buffer management, the eNB may perform rate
matching assuming for each component carrier, number of incremental
redundancy operations (N.sub.IR) may be calculated as follows:
N IR = N soft K C K MIMO min ( M DL_HARQ , M limit ) Eqn ( 1 )
##EQU00001##
in which N.sub.soft may represent the total number of soft channel
bits based on the UE category, as shown in column 408 of the table
in FIG. 4. If N.sub.soft=35982720, then K.sub.C may be equal to
five. Otherwise, if N.sub.soft=3654144 and the UE is capable of
supporting no more than a maximum of two spatial layers for the
downlink (DL) cell, K.sub.C may be equal to two. If none of the
above conditions holds, K.sub.C may be equal to one. K.sub.MIMO may
be equal to two if the UE is configured to receive physical
downlink shared channel (PDSCH) transmissions based on transmission
modes 3, 4, 8 or 9 (on a given CC). Otherwise, K.sub.MIMO may be
equal to one. M.sub.DL.sub.--.sub.HARQ may represent maximum number
of DL hybrid automatic repeat request (HARQ) processes (on a given
CC). M.sub.limit may be a constant, for example, equal to 8.
[0050] The UE may also determine number of soft channel bits and
store these bits for HARQ operation. For both frequency division
duplex (FDD) and time division duplex (TDD), if the UE is
configured with more than one serving cell, for each serving cell
and for at least K.sub.MIMOmin(M.sub.DL.sub.--.sub.HARQ,
M.sub.limit) transport blocks, upon decoding failure of a code
block of a transport block, the UE may store received soft channel
bits corresponding to a range of subframes, for example, at least
w.sub.k, W.sub.k+1, . . . ,
w.sub.mod(k+n.sub.SB.sub.-1,N.sub.cb.sub.), as follows:
n SB = min ( N cb , N soft ' C N cells DL K MIMO min ( M DL_HARQ ,
M limit ) ) , Eqn ( 2 ) ##EQU00002##
where w.sub.k may correspond to virtual circular buffer bits, C may
represent the number of coded blocks, M.sub.DL.sub.--.sub.HARQ may
represent the maximum number of DL HARQ processes,
D.sub.cells.sup.DL may represent number of configured serving
cells, N'.sub.soft may represent total number of soft channel bits
according to the UE category. In determining k, the UE may give
priority to storing soft channel bits corresponding to lower values
of k. w.sub.k may correspond to a received soft channel bit. The
range w.sub.k, w.sub.k+1, . . . ,
w.sub.mod(k+n.sub.SB.sub.-1,N.sub.cb) may include subsets not
containing received soft channel bits.
[0051] According to the Rel-10 of the LTE standard, maximum number
of DL HARQ processes may be defined as follows: For FDD, there may
be a maximum of eight downlink HARQ processes per serving cell. For
TDD, the maximum number of downlink HARQ processes per serving cell
may be determined by the UL/DL configuration, as indicated in the
table illustrated in FIG. 5.
[0052] FIG. 5 illustrates a table containing maximum number of DL
HARQ processes for each TDD UL/DL configuration as described in
Rel-10 of the LTE standard. As shown, different UL/DL
configurations may support different number of DL HARQ processes.
For example, the TDD UL/DL configuration 0 may support up to four
DL HARQ processes, whereas TDD UL/DL configuration 5 may support up
to fifteen DL HARQ processes.
[0053] The maximum number of DL HARQ processes for FDD and TDD as
defined in the LTE standard are determined based on the assumption
that all downlink subframes available for PDSCH transmissions for a
UE. However, in reality, a subframe may not be available for any
PDSCH for a UE or a group of UEs (e.g., either by specification or
by configuration). For example, in TDD, there may not be a PDSCH
transmission in DwPTS (downlink pilot time slot) of special
subframes in configurations 0 and 5 with normal downlink cyclic
prefix (CP), or configurations 0 and 4 with extended downlink CP.
Therefore, by specification, some or all of the UEs may not have
PDSCH transmission in the special subframes.
[0054] As another example, Rel-8 and/or Rel-9 UEs may not have any
PDSCH transmissions in multimedia broadcast/multicast services over
a single frequency network (MBSFN) subframes. However, Rel-10 UEs
may have PDSCH transmissions in the MBSFN subframes. In addition, a
UE may be indicated not to monitor some subframes for PDSCH, e.g.,
almost blank subframes (ABS). Or, a UE may be configured not to
monitor a set of subframes for any PDSCH transmission. For certain
aspects, each UE may be configured differently or, a group of UEs
may be configured to use or not use a set of subframes for PDSCH
transmissions.
[0055] For certain aspects, when some subframes are unavailable for
PDSCH for a UE (regardless of the reason), the maximum number of DL
HARQ processes may effectively be reduced. Therefore, the maximum
number of DL HARQ processes may be smaller than what is currently
specified by the standard. For certain aspects, for soft buffer
management at both the eNB and the UE sides, a smaller maximum
number of DL HARQ processes may imply a larger soft buffer size
(e.g., that may be used for rate matching) for each HARQ process,
which may improve DL throughput. The positive impact may be more
evident when the UE is configured with two or more component
carriers. If the UE is configured with two or more CCs, the total
soft channel bits may be split (e.g., either evenly or unevenly)
across all the configured CCs. Therefore, size of the soft buffer
may become relatively small for each CC.
[0056] Certain aspects of the present disclosure propose a method
for calculating number of soft buffer bits for hybrid automatic
repeat request (HARQ) operation by only taking into account the
subframes which are available for PDSCH for a UE or a group of UEs.
In the proposed method, the subframes that are unavailable for
PDSCH for at least a UE (e.g., either by specification or by
configuration) may not be considered in calculating the number of
soft buffer bits.
[0057] FIG. 6 illustrates example operations that may be performed
by a UE or a base station for soft buffer management in HARQ
operation. The operations may begin at 602 by determining for each
component carrier, number of downlink subframes available for a
physical downlink shared channel (PDSCH). At 604, the UE or the BS
may then determine at least one of a maximum number of downlink
hybrid automatic repeat request (HARQ) processes or size of a soft
buffer based at least on the number of downlink subframes available
for PDSCH. For certain aspects, the subframes that are unavailable
for a PDSCH may not be considered in determining the maximum number
of downlink HARQ processes or size of the soft buffer. For certain
aspects, size of the soft buffer may be different for different
component carriers.
[0058] For certain aspects, the subframes unavailable for PDSCH may
be special subframes that are configured not to transmit any PDSCH
in TDD mode. For certain aspects, number of subframes available for
(or not available) PDSCH may be the same for a plurality of user
equipments. For another aspect, the number of subframes available
for (or not available for) PDSCH may be different for different
UEs. For example, number of downlink subframes available for PDSCH
may be determined for a first UE and a second UE. The number of
subframes available for PDSCH may be specific to each of the first
and the second UEs (e.g., UE-specific). For example, a downlink
subframe may be available for a PDSCH for a first UE, but, the same
subframe may not be available for a PDSCH for a second UE.
[0059] As an example, there may not be any PDSCH transmission in
DwPTS of a special subframe (e.g., for special subframe
configurations 0 and 5 with normal downlink CP, or configurations 0
and 4 with extended downlink CP). Therefore, based on the proposed
method, the maximum number of DL H-ARQ processes may be calculated
as shown in the table in FIG. 7.
[0060] FIG. 7 illustrates an example table showing the benefits of
the proposed soft buffer management, in accordance with certain
aspects of the present disclosure. The table illustrates TDD UL/DL
configuration 702, maximum number of HARQ processes 704
(considering the special subframes as defined in Rel-10 of the LTE
standard), maximum number of HARQ processes 706 (without
considering the special subframes, the proposed scheme), difference
of max number of HARQ processes 708 in the proposed scheme and the
default scheme, and percentage of increase in soft buffer size per
HARQ process 710 in the proposed scheme.
[0061] This table shows a maximum number of DL HARQ processes
calculated with and without considering special subframes (e.g.,
configurations 0 and 5 with normal downlink CP or configurations 0
and 4 with extended downlink CP), and/or the subframes unavailable
for a PDSCH for a UE. For example, column 706 shows maximum number
of DL HARQ processes without considering special subframes
(according to the proposed scheme). To enable comparisons, special
subframes are taken into account during calculation of the maximum
number of DL HARQ processes (as defined in the LTE standard) shown
in column 704.
[0062] As can be seen in the example in FIG. 7, when the special
subframes which by configuration are unavailable for PDSCH for any
UE are not considered for calculating the maximum number of HARQ
processes, the maximum number of HARQ processes may be reduced
(e.g., by 2) for all the TDD downlink/uplink configurations.
Reduction in the maximum number of HARQ processes may result in an
increase in the number of soft buffer bits available for each DL
HARQ process. For example, for the UL/DL configuration 0, the
maximum number of HARQ processes in the proposed method is equal to
two (column 706). Whereas, in the LTE standard (column 704), the
maximum number of HARQ processes is equal to four. As a result, the
total number of available soft buffer bits for the UE may be
divided between two HARQ processes for the proposed method. The
same number of available soft buffer bits may be divided among four
HARQ processes, according to the LTE standard. Therefore, in this
example, the proposed scheme may result in 100 percent increase in
the number of soft buffer bits available for each HARQ process. As
another example, for UL/DL configuration 3, the proposed scheme may
result in 14 percent increase in the number of available soft
buffer bits for each HARQ process. It should be noted that for
configurations 2, 4 and 5, there is no increase in size of the soft
buffer per each HARQ process (due to the M.sub.limit/operation in
equations 1 and 2). However, as described earlier, for other
configurations the number of soft buffer bits for each HARQ process
may increase (e.g., between 14 to 100 percent).
[0063] As described earlier, for certain aspects, while managing
soft buffers, maximum number of DL HARQ processes may be determined
without considering some subframes which, by specification or by
configuration, are not available for any PDSCH for a UE or a group
of UEs. One particular example may be special subframes, which by
configuration are not available for any PDSCH for the UEs.
[0064] For certain aspects, maximum number of DL HARQ processes may
be calculated for each component carrier if there are two or more
CCs that are configured for a UE. For example, in Rel-10 TDD,
different CCs may have different configurations of special
subframes (e.g., some CCs may have special subframes configured as
unavailable for any PDSCH, while some may have special subframes
configured as available for PDSCH). Therefore, different component
carriers may have similar or different maximum number of DL HARQ
processes, depending on their specific configuration.
[0065] As another example, in future generations of wireless
systems, different CCs may have different TDD downlink/uplink
configurations, different system types (e.g., FDD, TDD, and the
like) or different configurations of MBSFN subframes, and the like.
Therefore, as described herein, different number of HARQ processes
may be calculated for different component carriers in which some of
the subframes may or may not be considered in calculating the
maximum number of HARQ processes for each component carrier.
[0066] For certain aspects, in order to maintain backward
compatibility (e.g., maintain compliance with previous releases
(e.g., Releases 8-10) of the LTE standard), it may be desirable to
keep a conventional soft buffer management for at least one fully
backward-compatible serving cell. Therefore, at least one
communication link may be maintained between the eNB and the UE to
ensure robust operation. For certain aspects, the proposed soft
buffer management scheme may be activated only when the UE is
configured with two or more cells. For example, the primary cell
may be fully backward compatible and the proposed scheme may be
applied to secondary cells. As an example, a UE may be configured
to communicate via two or more component carriers (e.g., a primary
component carrier and one or more secondary component carriers).
Therefore, size of the soft buffer may be determined for the
secondary component carriers based on the proposed method. For
another aspect, the proposed soft buffer management scheme may be
enabled only for extension carriers (e.g., carriers that are not
backward compatible). However, it should be noted that such
limitations are not preferable.
[0067] In this disclosure, a soft buffer management scheme is
proposed in which during calculation of the maximum number of HARQ
processes (and hence size of soft buffers) the subframes available
for PDSCH may be considered. Therefore, the subframes that are not
available for a PDSCH (e.g., either by specification or by
configuration) may not be considered. The proposed soft buffer
management scheme may result in increased soft buffer size per HARQ
process, which may improve performance of the HARQ process.
[0068] FIG. 8 illustrates an example network 800 comprising a base
station and a user equipment, in which the proposed method may be
utilized. The base station 810 may receive signals from the UE 820
and/or other base stations in its vicinity (not shown) using
receiver unit 816. The base station may process the received
signals using the soft buffer management module 814. In addition,
the base station may determine maximum number of HARQ processes
and/or size of a soft buffer based at least on the number of
subframes available for PUSCH. For certain aspects, the subframes
that are not available for a PUSCH may not be considered. The base
station may then transmit a signal using the transmitter module 812
and communicate with the UE on one or more component carriers using
HARQ operations. The UE 820 may receive a signal from the base
station using the receiver module 822. Similar to the BS, the UE
may determine, using the soft buffer management module 824, maximum
number of downlink HARQ processes and/or size of a soft buffer for
the UE based at least on the number of subframes available for
PDSCH. For certain aspects, the subframes that are not available
for a PDSCH may not be considered. The UE may then transmit signals
to the BS 810 using the transmitter module 826 and perform HARQ
operations with the BS, using the soft buffers.
[0069] It should be noted that although most of the examples in
this disclosure refer to downlink HARQ operation and soft buffer
management at the UE, similar ideas may be applied to other types
of wired or wireless devices (e.g., base stations) for managing
buffers, all of which would fall within the scope of the present
disclosure.
[0070] The various operations corresponding to blocks illustrated
in the method of FIG. 6 described above may be performed by various
hardware and/or software component(s) and/or module(s). For
example, means for determining may be any suitable processing
component, such as a processor 230 and/or processor 270, as shown
in FIG. 2.
[0071] The various illustrative logical blocks, modules and
circuits described in connection with the present disclosure may be
implemented or performed with a general purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array signal (FPGA) or
other programmable logic device (PLD), discrete gate or transistor
logic, discrete hardware components or any combination thereof
designed to perform the functions described herein. A general
purpose processor may be a microprocessor, but in the alternative,
the processor may be any commercially available processor,
controller, microcontroller or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0072] The steps of a method or algorithm described in connection
with the present disclosure may be embodied directly in hardware,
in a software module executed by a processor, or in a combination
of the two. A software module may reside in any form of storage
medium that is known in the art. Some examples of storage media
that may be used include random access memory (RAM), read only
memory (ROM), flash memory, EPROM memory, EEPROM memory, registers,
a hard disk, a removable disk, a CD-ROM and so forth. A software
module may comprise a single instruction, or many instructions, and
may be distributed over several different code segments, among
different programs, and across multiple storage media. A storage
medium may be coupled to a processor such that the processor can
read information from, and write information to, the storage
medium. In the alternative, the storage medium may be integral to
the processor.
[0073] The methods disclosed herein comprise one or more steps or
actions for achieving the described method. The method steps and/or
actions may be interchanged with one another without departing from
the scope of the claims. In other words, unless a specific order of
steps or actions is specified, the order and/or use of specific
steps and/or actions may be modified without departing from the
scope of the claims.
[0074] The functions described may be implemented in hardware,
software, firmware or any combination thereof. If implemented in
software, the functions may be stored as one or more instructions
on a computer-readable medium. A storage media may be any available
media that can be accessed by a computer. By way of example, and
not limitation, such computer-readable media can comprise RAM, ROM,
EEPROM, CD-ROM or other optical disk storage, magnetic disk storage
or other magnetic storage devices, or any other medium that can be
used to carry or store desired program code in the form of
instructions or data structures and that can be accessed by a
computer. Disk and disc, as used herein, include compact disc (CD),
laser disc, optical disc, digital versatile disc (DVD), floppy
disk, and Blu-ray.RTM. disc where disks usually reproduce data
magnetically, while discs reproduce data optically with lasers.
[0075] Software or instructions may also be transmitted over a
transmission medium. For example, if the software is transmitted
from a website, server, or other remote source using a coaxial
cable, fiber optic cable, twisted pair, digital subscriber line
(DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of transmission
medium.
[0076] Further, it should be appreciated that modules and/or other
appropriate means for performing the methods and techniques
described herein can be downloaded and/or otherwise obtained by a
user terminal and/or base station as applicable. For example, such
a device can be coupled to a server to facilitate the transfer of
means for performing the methods described herein. Alternatively,
various methods described herein can be provided via storage means
(e.g., RAM, ROM, a physical storage medium such as a compact disc
(CD) or floppy disk, etc.), such that a user terminal and/or base
station can obtain the various methods upon coupling or providing
the storage means to the device. Moreover, any other suitable
technique for providing the methods and techniques described herein
to a device can be utilized.
[0077] It is to be understood that the claims are not limited to
the precise configuration and components illustrated above. Various
modifications, changes and variations may be made in the
arrangement, operation and details of the methods and apparatus
described above without departing from the scope of the claims.
[0078] While the foregoing is directed to embodiments of the
present disclosure, other and further embodiments of the disclosure
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *